1. Field
The present invention relates to tire treads and notably to the sipes with which these treads may be provided. It also relates to the treads comprising inserts intended to form new grooves after these treads have become partially worn, these treads also comprising sipes according to the invention.
2. Description of Related Art
It is known practice to form a tread having a tread surface that is intended to come into contact with a roadway, this tread having sufficient thickness to allow a satisfactory service distance to be covered through wear. It is known practice to provide the tread of a tire intended to be fitted to a passenger vehicle with a plurality of grooves the depth of which is suited to the grooves being present and effective throughout the service life. In combination with these grooves there are a plurality of sipes which make it possible to generate a great many edge corners of material without, however, excessively reducing the stiffness of the tread and without excessively increasing the voids volume of this tread.
In order to obtain in the initial state (which means as it leaves the mold) a suitable level of stiffness while at the same time ensuring a high number of voids at the end of life so that the tire has a great deal of wet grip, it has been proposed that new grooves be generated once tire wear reaches a certain level by either forming channels inside the tread or by introducing into the tread at least one insert which, when removed, forms a new grooves as described for example in patent document BE-399026-A.
In the latter instance, it is advantageous to combine both the presence of at least one insert and a plurality of sipes the orientation of which intersects the orientation of the insert.
During testing it has been found that movements of unvulcanized material can occur during the tire molding operation; these movements of material are not without impact on the geometry of the constituent parts and, more particularly of the inserts themselves that is obtained, and this can lead to a reduction in the running performance of the tire. In particular, it has been found that, with wear of the tread, the switchover from the sipe to the new groove formed by the insert is sometimes nonuniform and that can present problems.
It is an object of the invention to prevent such a problem.